Oil system, in particular a hydraulic or lubricating oil system

ABSTRACT

The invention relates to an oil system, in particular a hydraulic oil system or a lubricating oil system, comprising a sensor for monitoring the impurity content of the oil in the oil system, the sensor detecting a value which is correlated with the impurity content. A particularly cost-effective construction is achieved, if the sensor is configured as a turbidity sensor which measures the turbidity of the oil, which has been caused by the impurity content.

CROSS REFERENCE TO RELATED APPLICATIONS

Applicants claim priority under 35 U.S.C. §119 of German Application No.199 57 592.4 filed Nov. 30, 1999. Applicants also claim priority under35 U.S.C. §120 of PCT/DE00/04234 filed Nov. 29, 2000. The internationalapplication under PCT article 21(2) was not published in English.

This invention relates to an oil system, in particular a hydraulicsystem or a lubricating oil system, having the features of the preambleof claim 1. This invention also relates to a filter for such an oilsystem as well as the use of a turbidity sensor in such an oil system.

Hydraulic oils and lubricating oils should be designed to beenvironmentally friendly, in particular biodegradable, for reasons ofenvironmental safety. These conditions lead to oils having acomparatively low stability with respect to hydrolytic cleavage incontact with water. Therefore, in the case of oils, in particularrapidly biodegradable oils, but also traditional mineral oils, a lowwater content makes a considerable contribution to a long oil standingtime. An unacceptably high water content can lead to aging products,especially by way of hydrolysis, and can cause material problems andfunction problems in the equipment supplied or working with these oils.Likewise, serious damage or functional disorders may be caused inhydraulic systems due to thermal decomposition of the oil, due todissolution or due to chemical attack on components. Such damage can beprevented by a sensor which detects the impurity content in oil, e.g.,by shutting down the oil system promptly.

British Patent 2,194,333 A describes a sensor for monitoring theimpurity content in an oil. The sensor senses a value which correlateswith the impurity content and is configured as a turbidity sensor whichmeasures the turbidity of the oil which occurs as a function of theimpurity content. To this end, the oil to be monitored, or at least apartial stream thereof, is passed through a measuring distance in whichlight is beamed into the oil to be monitored. The light transmitted bythe oil in the measuring distance is measured and a signal value thatcorrelates with the impurity content is generated as a function of themeasured intensity of the transmitted light, and this signal value isused to monitor the impurity content in the oil.

U.S. Pat. No. 4,499,376 discloses a device for measuring a particleimpurity in a liquid, whereby the measurements are based on thepermeability of the liquid for infrared light. Accordingly, an infraredsensor measures a turbidity of the liquid which occurs as a function ofthe impurity content and it generates electric signals that correlatewith it.

U.S. Pat. No. 5,599,460 describes a filter for an oil system whichcontains in a housing a filter element and a sensor for monitoring theimpurity content in the oil. The sensor is situated upstream from thefilter element in the housing.

In their article “Perspectives for environmentally friendly hydraulics,”printed on pages 352 through 367 of the journal “o+p Ölhydraulik undPneumatik” [Oil Hydraulics and Pneumatics], vol. 41 (1997) no. 5, onpage 359, Kempermann, Remmelmann and Werner present an oil system inwhich a hydraulic pump connected to a reservoir on the intake sidesupplies oil to a feeder line on the pressure side. This feeder linecarries the oil to a hydraulic system that is driven or operates withthe oil. Downstream from this hydraulic system, the oil is sent back toa reservoir. Downstream from the hydraulic pump and upstream from thehydraulic system, a bypass line is connected to the feeder line; anelectromagnetically switchable valve is situated in this bypass line anddownstream from this valve there is a water-absorbent filter element.The bypass line also opens into a reservoir, bypassing the hydraulicsystem. Upstream from the hydraulic system, a sensor is arranged in thefeeder line upstream from the bypass connection; this sensor monitorsthe water content in the oil and detects when it exceeds a saturationlimit.

The sensor used for this purpose determines the increase in flowresistance of a pilot stream through a layer of water-absorbent starchpolymers. If the pressure medium occurs, i.e., the hydraulic oil,becomes oversaturated, the polymer swells due to uptake of water. Theelevated pressure acts on a differential pressure switch which thusdelivers the desired warning signal. To this extent, this sensor sensesa value which correlates with the water content of the oil.

The sensor is connected to the above-mentioned valve, which blocks thebypass in a first switch position and opens it in a second switchposition. As soon as the sensor senses that the saturation limit hasbeen reached, the sensor switches the valve, thus opening the bypass, sothat the oil contaminated with an elevated water content flows throughthe filter element. In this way, the unwanted water content of the oilcan be reduced.

In “MSR Magazine” 1-2/199, pages 10 and 11, Lauri Tuomaala reports onmethods of measuring the moisture content or the water content of theoil in a lubrication system of a paper machine. By monitoring the watercontent of the oil in the lubrication system in combination withcorresponding measures to reduce the water content of the oil, themaintenance costs of an installation equipped with this lubricationsystem can be greatly reduced and the useful life of the installationcan be prolonged. To monitor the water content, a measuring transduceror sensor is used, measuring the water content of the oil on the basisof the water activity. The water activity correlates with the watercontent of the oil.

In order for a washing machine for washing clothing items to have thelowest possible water consumption for ecological reasons, modern washingmachines may be equipped with a turbidity sensor which measures thedegree of soiling of the wash water. As long as the degree of soiling ofthe wash water used for cleaning items of clothing remains below acertain threshold value, the wash water need not be replaced by freshwater. In this way, the water consumption of this washing machinedepends on the degree of soiling of the laundry washed with it.

The present invention is concerned with the problem of providingexpedient options for an oil system of the type defined in the preamblethat will permit economical monitoring of the impurity content in oil.

This problem is solved according to this invention by an oil systemhaving the features of claim 1.

This invention is based on the general idea of using an essentiallyknown turbidity sensor, which operates on an optical principle, formonitoring the impurity content in oil. In doing so, this invention ismaking use of the finding that the impurity content in oil also causes avisually detectable turbidity which correlates with the impurity contentof the oil. This finding is surprising at least inasmuch as oil, incomparison with water, is relatively impermeable for visible light. Itwas surprising to discover that water, whose light permeability isusually greater than that of oil, can cause turbidity in oil under thespecific conditions prevailing in an oil system. Liquids, in particularwater, lead to the development of finely distributed droplets in the oilor form a type of emulsion under the operating conditions of an oilsystem (oil pressure, flow conditions, turbulence). Optical effects inparticular, such as refraction and movement of light at the mediaboundaries, then result in turbidity of the oil.

The term “turbidity” is understood here to refer to a reducedpermeability or transmission of the oil for beams of light, inparticular for infrared light. Since the light permeability of water andoil differ greatly, especially in the infrared range, an increasingwater content causes a decrease in the transmission of infrared lightand thus an increase in the turbidity of the oil.

Since such turbidity sensors are essentially known and are availablecommercially at low cost, this yields a price advantage for the oilsystem according to this invention. In addition, experiments have shownthat the turbidity sensor operates relatively inaccurately and respondseven at a relatively low impurity content or water content in the oil.

According to a preferred embodiment, the turbidity sensor may besituated upstream from a switching valve in a feeder line, the switchingvalve in a first switch position supplying the oil to an equipmentarrangement that operates with and/or is supplied with oil through thefeeder line, and in a second switch position supplying the oil into abypass line where an element suitable for reducing the impurity contentof the oil flowing through it is situated, whereby the turbidity sensoror a control unit communicating with the turbidity sensor actuates theswitching valve. Due to this arrangement, the turbidity sensor can causethe switching valve to switch to the bypass line as soon as a thresholdvalue for the impurity content is reached. On the other hand, thisarrangement also makes it possible to switch the switching valve backfor supplying the equipment arrangement as soon as the impurity contentdrops back to an allowed range again.

The problem on which the invention is based is also solved by a filterhaving the features of claim 8. By integration of the sensor and theelement which reduces impurities into a filter housing and by arrangingthe sensor inside the housing upstream from a filter element, thisyields an especially compact design which also guarantees that thefilter element does not have a negative effect on the measurement of theimpurity content in oil.

The problem on which the invention is based is also solved by a methodhaving the features of claim 9. This method makes use of the findingthat under the conditions prevailing in an oil system, light, especiallyinfrared light, passes through the oil essentially unhindered while itis absorbed or scattered by water to varying degrees. Accordingly, thetransmission of light through the oil changes as a function of the watercontent. By analysis of the transmission; the water content of the oilcan be monitored, and through corresponding actuation of the switchingvalve, the water content may optionally be reduced.

The problem on which this invention is based is ultimately solved byusing a turbidity sensor according to the features of claim 12. Thismakes use of the finding that the sensor, which is designed fordetecting turbidity in water, can essentially also be used to detect animpurity content, in particular a water content, in oil under theoperating conditions of an oil system, especially if the sensor operateswith infrared light. Since such a turbidity sensor is known per se,monitoring of the water content of the oil of an oil system can beimplemented in an especially economical manner.

Other important features and advantages of the device according to thisinvention are derived from the subclaims, from the drawings and from therespective description of the figures on the basis of the drawings.

Preferred embodiments of this invention are illustrated in the drawingsand are explained in greater detail in the following description.

The drawings show schematically:

FIG. 1 a block diagram like a schematic of a first embodiment of an oilcircuit designed according to this invention;

FIG. 2 a diagram like that in FIG. 1, but a second embodiment;

FIG. 3 a sectional view through a filter in a first embodiment designedaccording to this invention;

FIG. 4 a simplified block diagram of a filter according to FIG. 3, butin another embodiment;

FIG. 5 a diagram like that in FIG. 4, but in another embodiment;

FIG. 6 a block diagram of a turbidity sensor, and

FIG. 7 a detail view according to VII in FIG. 6 in a special embodiment.

Since the use of a turbidity sensor to monitor the water content of oilin an oil system is of primary importance, the embodiments describedbelow are always explained with respect to a turbidity in the oil due tothe presence of water. However, it is self-evident that the turbiditysensor is essentially suitable for monitoring any turbidity in oil,regardless of its cause. For example, the carbon black content of therespective oil can be monitored. Examples of oils whose soiling orturbidity is to be monitored include, for example, lubricating oil,motor oil, heating oil and diesel oil. Applications in motor vehicles,e.g., to monitor the soiling of the motor oil or the fuel, whethergasoline or diesel, are also of interest. For example, the carbon blackcontent of motor oil can be monitored in a vehicle to thereby determinethe degree of soiling of an oil filter.

According to FIGS. 1 and 2, an oil system 1 according to this inventionhas an oil reservoir 2 from which an oil pump 3 draws oil. The oil pump3 is connected at the intake side to the reservoir 2 by an intake line4. At the pressure side the oil pump 3 conveys oil into a feeder line 5which delivers oil to an equipment arrangement 6 which needs the oil.The equipment arrangement 6 may be a machine or a machine installation,for example, which is supplied with oil for lubrication. Oil system 1then forms a lubricating oil system. Likewise, the equipment arrangement6 may be a single hydraulic unit or a complete hydraulic system, e.g., amachine. In this case, oil system 1 forms a hydraulic oil system.

Downstream from the equipment arrangement 6, the oil is returned to thereservoir 2 through a return line 7. Upstream from the equipmentarrangement 6, an oil filter 8 is provided in the feeder line 5 tofilter out the conventional impurities, especially suspended particlesor the like, out of the oil. A switching valve 9 which is situatedbetween the oil filter 8 and the oil pump 3 can be switched between atleast two switch positions by means of an electromagnetic controlelement 10. In a first switch position, the switching valve 9 connectsthe pressure side of the pump 3 to the section of the feeder line 5leading to the equipment arrangement 6. In a second switch position, theswitching valve 9 connects the pressure side of the pump 3 to a bypassline 11, which leads back to the reservoir 2, bypassing the oil filter 8and the equipment arrangement 6. A water extracting element 12 issituated in this bypass line 11 to reduce the water content of the oilas the oil flows through it. Downstream from the water extractingelement 12, the bypass line 11 may be connected to the feeder line 5 bya supply line 13, represented with a broken line, downstream from theoil filter 8 in a special embodiment. In this way, the equipmentarrangement 6 may also be supplied with oil (from which the water hasbeen removed) when the switching valve 9 is in its second switchposition. Likewise, a mixed conveyance of the dehydrated oil downstreamfrom the water extracting element 12 is also possible, whereby the oilis sent partially to the equipment arrangement 6 and partially to thereservoir 2; the corresponding valve means are not shown here.

Between the switching valve 9 and the oil pump 3, a sensor 14communicates with the oil conveyed. This sensor 14 may communicate withthe feeder line 5 through a corresponding connecting line 15, as shownin FIGS. 1 and 2. However, embodiments in which the sensor 14 issituated directly in the oil flow are preferred, whereby it may beintegrated into the feeder line 5, for example. The sensor 14 monitorsthe water content of the oil and actuates the switching valve 9 over acorresponding line 16 as soon as the water content of the oil hasreached a critical level. According to this invention, the sensor 14 isdesigned as a turbidity sensor whose functioning is described furtherbelow, specifically in conjunction with FIG. 6.

Although the arrangement of the sensor 14 upstream from the switchingvalve 9 as selected here is preferred, it may be quite appropriate tomount the sensor 14 at another location in the oil system 1, e.g., inthe reservoir 2 or in the return line 7.

The embodiments in FIGS. 1 and 2 differ in the type of water extractingelement 12. In the embodiment according to FIG. 1, the water extractingelement 12 is an absorber which may be designed in the form of a filterelement. The absorber stores the water extracted from the oil. A waterextracting element 12 designed as an absorber contains, for example, agel-filled filter element which forms a chemical bond with the waterremoved from the oil. In contrast with that, in the embodiment accordingto FIG. 2, the water extracting element 12 is formed by a coalescer,which separates the water from the oil as the oil laden with water flowsthrough it, and allows the water to flow out of the oil flow. The waterremoved in this way may be collected in a separate container 17. Sinceboth absorbers and coalescers are known in general, a more extensivedescription of these components may be omitted.

The oil system 1 presented in the embodiments in FIGS. 1 and 2 functionsas follows:

In normal operation, the oil contains an allowed amount of impurities,in particular water, so that the turbidity sensor 14 or a controllerconnected to it switches the switching valve 9 into its first switchposition. Accordingly the oil flows through the oil filter 8 to theequipment arrangement 6. Since the bypass line 11 does not have flowthrough it in normal operation, no flow can develop through the waterextracting element 12, so that it is protected in normal operation andis ready for use for emergency operation.

As soon as the turbidity sensor 14 detects an inadmissibly high impuritycontent or water content in the oil, the switching valve 9 is switchedinto its second switch position, thereby activating emergency operation.The oil, which is loaded with water, is then sent to bypass 11 and flowsthrough the water extracting element 12. This emergency operation ismaintained until the turbidity sensor 14 again senses an admissibleimpurity content or water content and switches back to normal operationor the switching valve 9 switches to its first switch position.

Since a traditional oil filter may also have the property of extractingwater from the oil, the oil filter 8 may become rapidly saturated whenthe water content is inadmissibly high. This can be avoided because thebypass 11 bypasses the oil filter 8.

According to FIGS. 3, 4 and 5, a filter 18 according to this inventionhas a housing 19 in which is arranged a filter element 20. The filterelement may be an oil filter element, so that this filter 18 forms anoil filter, which corresponds to the oil filter 8 of the oil system 1shown in FIGS. 1 and 2, for example. Likewise, the filter element 20 maybe an absorber filter element.

In the housing 19 of the filter 18, the turbidity sensor 14 is situatedupstream from the filter element 20. An analyzer unit or a controller 21of the turbidity sensor 14 is then connected to the switching valve 9over the line 16.

According to a preferred embodiment illustrated in FIG. 4, switchingvalve 9 may be integrated into the housing 19 of the filter 18. Inaddition, both the oil filter 8 and the water extracting element 12 aredesigned in the housing 19, with separate flow paths being designed inthe interior of the housing 19 accordingly. In normal operation, theswitching valve 9 switches an inlet 22 of the filter 18 to the oilfilter 8, and in emergency operation, it switches to the waterextracting element 12. With the embodiments illustrated in FIG. 5, thefilter housing 19 has only one outlet 23; likewise, an embodiment withtwo outputs may be provided.

The embodiments of FIGS. 4 and 5 differ essentially in the type of waterextracting element 12, which is preferably formed by an absorber in thevariant according to FIG. 4 and by a coalescer in the variant accordingto FIG. 5.

According to FIG. 6, a turbidity sensor 14 according to this inventionhas a bolt-like sensor section 24 and a control unit 25, which maycontain electronics 26 as well as a controller, an analyzer unit and thelike. The sensor 14 is mounted so that its sensor section 24 projectsinto a space 27 through which the oil to be monitored flows, the controlunit 25 may be situated outside the space 27. Accordingly, the sensorsection 24 penetrates through the housing 19, for example.

The sensor 14 has in its sensor section 24 a measuring distance 28 whichis open toward the space 27 and accordingly is penetrated by the oil inspace 27 or through which the oil may flow. In addition, there is atleast one sensor 29 which beams light, preferably infrared light, intothe measuring distance 28 and thus into the oil in it. The infraredlight passes through the measuring distance 28 and in general strikes atleast one receiver 30, which senses the incoming light intensity. Thetransmission of the infrared light through the measuring distance 28 andthrough the oil in it is represented symbolically by an arrow 31 in FIG.6.

Transmitter 29 and receiver 30 are connected to the control unit 25, inwhich an analyzer unit, for example, may generate a signal value thatcorrelates with the transmission 31. Since certain wavelengths of lightare preferred for the beam of light, in particular in the infraredrange, the beam of light may pass almost unhindered through oil whichdoes not have any turbidity, whereas the beam of light is increasinglyhindered with an increase in water content, i.e., with increasingturbidity. In other words, the greater the water content of the oil, theless light can be sensed by the receiver 30. The reduction in theinfrared light transmission with an increase in the water content is theresult of an absorption effect of the water with respect to infraredlight on the one hand, while on the other hand, the water in the oilsystem regularly occurs as an emulsion in the oil, so that diffraction,refraction and dispersion effects can also interfere with thetransmission.

Experiments have shown that in operation with light at a wavelength of750 nm to 1000 nm, preferably 880 nm, the sensor 14 has an especiallyhigh sensitivity with regard to water present in the oil, so that arelatively low water content can be detected in the oil.

FIG. 7 shows a detail of the sensor 14, designated as VII in FIG. 6, onan enlarged scale, but in a preferred embodiment. The sensor 14 here hasa transmitter unit 29 which has two transmission sites 32. Thesetransmission sites 32 may be formed by two apertures, for example, whichare acted upon by a common transmitter. Likewise, a separate transmittermay also be provided for each transmission site 32. In addition, thesensor 14 has a receiver unit 30, which has two receiver sites 33. Hereagain, the receiver sites 33 may be formed by apertures which share acommon receiver. As an alternative, the receiver sites 33 may each beprovided with a separate receiver.

The measuring distance 28 formed between the transmitter unit 29 and thereceiver unit 30 communicates with the space 27 so that the measuringdistance 28 may receive the oil to be monitored. In addition, twoseparate signal paths or light paths 34 and 35 are provided between thetransmitter unit 29 and the receiver unit 30, symbolized here by dottedlines. The two signal paths 34, 35 differ from one another with regardto the length of their segments 36 and 37 with which they run inside themeasuring distance 28, i.e., through the oil to be monitored. In thepresent case, the two signal paths 34 and 35 run at least partiallyinside of the measuring distance 28. Likewise, an embodiment in whichthe one signal path 34 runs completely outside the measuring distance 28is also possible. The different lengths of their segments 36 and 37 areachieved here by a step 38 which projects into the measuring distance28. A light-permeable line 39 is formed in this step 38, e.g., in theform of a borehole or an optical fiber.

With the help of this arrangement, the degree of soiling may bedetermined from a comparison of the received signals sensed at thereception sites 33. Therefore, the measurement is independent offluctuations in current or voltage or aging phenomena in the transmitterunit 29 or in the receiver unit 30, because they act in the same waywith both signal paths 34, 35. In addition, this arrangement may also beused to monitor proper functioning of the sensor 14. Due to thedifferent lengths of the segments 36 and 37, the received signals thatcan be sensed in the case of turbidity are necessarily different withthe two signal paths 34, 35. With increasing turbidity, the two receivedsignals drop to different extents according to a first functionalrelationship. When the transmission power of the transmitter unit 29drops because of a fluctuation in current, for example, this results inboth received signals decreasing according to a second functionalcorrelation. This difference can be recognized by a correspondinganalyzer device.

What is claimed is:
 1. An oil system, in particular a hydraulic system or a lubricating oil system, having a sensor (14) for monitoring the impurity content in the oil in the oil system (1), which senses a value that correlates with the impurity content, whereby the sensor is designed as a turbidity sensor (14) which measures the turbidity of the oil which occurs as a function of the impurity content, whereby the turbidity sensor (14) is situated in a feeder line (5) upstream from an equipment arrangement (6) which is supplied with and/or works with oil, characterized in that the turbidity sensor (14) is arranged upstream from a switching valve (9) in the feeder line (5), whereby the switching valve (9) in a first switch position supplies the oil to the equipment arrangement (6), and in a second switch position it supplies oil to a bypass line (11) in which is arranged an element (12) suitable for reducing the impurity content in the oil flowing through the element, whereby the turbidity sensor (14) or a controller (21) which communicates with the turbidity sensor (14) actuates the switching valve (9).
 2. The oil system according to claim 1, characterized in that the turbidity sensor (14) generates a signal value which correlates with the turbidity which occurs due to the impurity content in the oil.
 3. The oil system according to claim 1, characterized in that the turbidity sensor (14) is arranged in the feeder line (5) upstream from a filter element (8).
 4. The oil system according to claim 1, characterized in that the element (12) suitable for reducing the impurity content is formed by an absorber or by a coalescer which reduces the liquid impurities content in the oil.
 5. The oil system according to claim 1, characterized in that the bypass line (11) in a reservoir (2) and/or downstream from the filter element (8) and upstream from the equipment arrangement (6) opens into the feeder line (5).
 6. The oil system according to claim 1, characterized in that the turbidity sensor (14) has at least one transmitter (29) and at least one receiver (30), between which is formed a measuring distance (28), which receives the oil to be monitored, and two separate signal paths (34, 35), whereby at least one of the signal paths (34, 35) runs inside the measuring distance (28), and whereby the two signal paths (34, 35) differ from one another with regard to the length of their segments (36, 37) within the measuring distance (28).
 7. The oil system according to claim 6, characterized in that to determine the signal value which correlates with the turbidity and/or to monitor for proper functioning of the turbidity sensor (14), the received signal received over the one signal path (34) is compared with the received signal received over the other signal path (35).
 8. A filter for an oil system, in particular according to claim 1, whereby the oil system (1) has a sensor (14) for monitoring the impurity content in the oil of the oil system (1), which senses a value that correlates with the impurity content, whereby the filter (18) has a housing (19) in which a filter element (8) is arranged for purifying the oil, whereby the sensor (14) is situated in the housing (19) upstream from the filter element (8) characterized in that an element (12) for reducing the impurity content in the oil is also arranged in the housing (19), whereby in addition, a switching valve (9) is also arranged in the housing (19), 50 that in a first switch position it connects an inlet (22) of the housing (19) to the oil filter element (8), and in a second switch position it connects the inlet (22) to the reducing element (12).
 9. A method of monitoring the impurity content in the oil of an oil system according to claim 1, whereby the oil to be monitored or at least a partial stream thereof is sent through a measuring distance (28); light is beamed into the oil to be monitored in the measuring distance (28); the light transmitted by the oil in the measuring distance (28) is measured; a signal value that correlates with the impurity content in the oil is generated as a function of the measured intensity of the transmitted light and is used to monitor the impurity content in the oil characterized in that for normal operation in which the oil has an admissible impurities content, the switching valve (9) is switched to the first switch position, in which the oil flows through an oil filter (8) to the equipment arrangement (6), whereby for emergency operation in which the oil has an inadmissibly high impurities content, the switching valve (9) is switched to the second switch position in which the oil flows through the bypass line (11) and the reducing element (12).
 10. The method according to claim 9, characterized in that the light used is infrared light which has a wavelength of 750 nm to 1000 nm, preferably 880 nm.
 11. The method according to claim 9, characterized in that to determine the signal value that correlates with the turbidity and/or to monitor for proper functioning of the turbidity sensor (14), a first measured intensity is compared with a second measured intensity, whereby the two intensities are assigned to different light paths (34, 35) which differ with regard to the length of their segments (36, 37) within the measuring distance (28).
 12. A use of a turbidity sensor (14) having a measuring distance (28) which is suitable for through-flow with a liquid to be monitored, having at least one transmitter (29) which beams light into the measuring distance (28) in the liquid, having at least one receiver (30) which measures the intensity of the light which is transmitted through the liquid in the measuring, distance (28) for carrying out the method according to claim
 9. 